same thing happened to me. We had warranty though so we got a new tv. I've seen this happen to many Sharp tvs
You have dead pixels. replace with warranty if you have. if not, stay away from sharp and invest in a samsung or sony. Besides, who uses a tv nowadays anyway. I does watch all meh entertainment pan meh GYALaxy phone. Tv only fa people who want impress guest. unless of course you enjoy porn on a 70".